Damping apparatus for bicycle forks

ABSTRACT

A bicycle fork having a damping apparatus that includes a cylinder, a damping fluid and a piston. The cylinder defines a chamber. The damping fluid is located in the chamber. The piston is disposed in the chamber and is positioned adjacent the fluid.

RELATED APPLICATION

This application is a continuation of Ser. No. 08/725,406, filed Oct. 3,1996, now U.S. Pat. No. 5,848,675 and a continuation of U.S. patentapplication Ser. No. 09/081,157, filed May 18, 1998, now U.S. Pat. No.6,241,060 entitled DAMPING APPARATUS FOR BICYCLE FORKS, the completedisclosure of which is hereby expressly incorporated by reference.

TECHNICAL FIELD

The present invention is directed to a damping apparatus for use withbicycle forks, the apparatus of the type that provides fluid damping.

BACKGROUND AND SUMMARY

Conventional bicycle forks connect a front wheel of a bicycle to abicycle frame so that the rider can rotate the front wheel and steer thebicycle. The bicycle fork typically includes a fork steerer tube that iseasily rotated by handlebars. The steerer tube is coupled to a forkcrown that extends across the top of the bicycle wheel. Two bladesextend from opposing ends of the fork crown on opposite sides of thewheel to securely attach the crown to opposite sides of an axle of thefront bicycle wheel.

Bicycle forks are not only used to steer bicycles, but they are alsoused to absorb various loads that are experienced by a front wheel ofthe bicycles. See, for example U.S. Pat. No. 5,445,401 to Bradbury.These conventional bicycle forks are known to include inner and outertelescoping members that are compressible toward one another andexpandable away from one another to absorb shock.

In rough terrain, however, these telescoping bicycle forks often reboundtoo rapidly after hitting a large bump. Some bicycle riders have alsofound that traditional telescoping bicycle forks compress too rapidlyupon hitting small bumps. Therefore, manufacturers of bicycle forks havedeveloped damping apparatuses that have damping mechanisms forcontrolling the relative movement between the telescoping members. See,for example U.S. Pat. No. 5,445,401. Although bicycle riders haveembraced damping bicycle forks, as riders maneuver their bicycles overrougher terrain for longer lengths of time heat build-up within thedamping fluid can cause some traditional forks to “seize” due topressure buildup in a closed system. This undesirable result has ledsome riders to use a damping apparatus that allows the damping oil tofreely circulate between the two telescoping legs. Such an apparatus,however adds unnecessary weight to the bicycle and is difficult todissemble. It would be beneficial to provide a damping apparatus that isincorporated into a bicycle fork that provides individual compressiondamping and rebound damping.

Accordingly, one illustrative embodiment provides a bicycle fork havinga damping apparatus. The damping apparatus comprises a cylinder, ashaft, damping fluid, and a piston. The cylinder defines a chamberwithin which the shaft is disposed. The damping fluid is located in thechamber. The piston is also disposed in the chamber and is coupled withthe shaft. The piston is movable relative to the shaft between first andsecond positions. The piston also has a fluid flow aperture disposedthere through and a valve structure associated with the piston. Thevalve structure is movable between engaged and disengaged positions. Thefluid flow aperture is occluded when the valve structure is engaged andis exposed when the valve structure is disengaged. The piston is movablefrom the first position to the second position as a result of anexternal force being applied to the fluid which acts on the piston. Whenthe piston is in the second position, the fluid is caused to movethrough the fluid flow aperture and move the valve structure to thedisengaged position. Further illustrative embodiments comprise a biasmember associated with the piston, the shaft including first and secondapertures in communication with each other with each aperture positionedon opposed sides of the piston. The first aperture is occluded when thepiston is in the first positioned and is exposed when the piston is inthe second position.

Another illustrative embodiment of the bicycle fork provides a dampingapparatus comprising a cylinder a damping fluid and a floating piston.The cylinder defines a chamber. The damping fluid is located in thechamber. The floating piston disposed in the chamber and is positionedadjacent the fluid.

Additional features and advantages of the apparatus will become apparentto those skilled in the art upon consideration of the following detaileddescriptions exemplifying the best mode of carrying out the apparatus aspresently perceived.

BRIEF DESCRIPTION OF THE DRAWINGS

The illustrative apparatus will be described hereinafter with referenceto the attached drawings, which are given as non-limiting, examplesonly, in which:

FIG. 1 is a perspective view of a bicycle fork that includes the dampingapparatus of the present invention;

FIG. 2 is a cross-sectional view of the damping apparatus showing thedamping apparatus having an upper leg formed for slidable extension intoa lower leg, compression piston unit mounted in the upper leg, a reboundpiston unit mounted on the lower leg and extending into the upper leg,and an oil bath situated in the upper leg between the compression andrebound piston units;

FIG. 3 is an exploded perspective view of a portion of the compressionpiston unit showing a coupler, a shim stack, a compression piston, amovable valve, a shaft, and a needle formed to extended into thecoupler;

FIG. 4 is an enlarged exploded perspective view of a portion of therebound piston unit showing a coupler, a shim stack, a rebound piston, amovable valve, a shaft, and a needle formed to extend into the coupler;

FIG. 5 is a cross-sectional view of the rebound piston taken along line5—5 of FIG. 4;

FIG. 6 is a diagrammatic illustration of the damping apparatus showingcompression of the upper leg into the lower leg;

FIG. 7 is a diagrammatic illustration of the damping apparatus showingthe upper leg as it moves out from the lower leg to an extendedposition;

FIG. 8 is a cross-sectional view of an alternative embodiment of thedamping apparatus of the present invention showing a compression pistonunit and an adjustable rebound piston unit;

FIG. 9 is another cross-sectional view of an alternative embodiment ofthe damping apparatus of the present invention showing a compressionpiston unit and a rebound piston unit;

FIGS. 10 and 11 are diagrammatic illustrations of another embodiment ofthe damping apparatus of the present invention showing the action of therebound piston blow-off valve on low velocity and high velocitycompression strokes;

FIG. 12 illustrates another embodiment of a compression piston unit fora damping apparatus according to the present invention;

FIG. 13 illustrates the compression piston unit of FIG. 12 when acompression force is applied to the damping, apparatus.

FIG. 14 is another alternative embodiment of a compression piston unitfor a damping apparatus according to the present invention;

FIG. 15 illustrates the embodiment of FIG. 14 when a compression forceis applied to the damping apparatus; and

FIG. 16 is a diagrammatic illustration of another embodiment of adamping apparatus according to the present invention.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplification set out hereinillustrates several embodiments of the apparatus and suchexemplification is not to be construed as limiting the scope of theapparatus in any manner.

DETAILED DESCRIPTION OF THE DRAWINGS

A damping apparatus 10 is formed for use in a suspension bicycle fork 12mounted between a bicycle frame (not shown) and a front wheel axle (notshown). The bicycle fork 12 includes a steerer tube 14, a crown 16, twoparallel fork legs 18, 19 and two brake flanges 20. Each brake flange 20has a brake arch receiver 22 at one end for mounting a brake arch (notshown) thereon and a rim brake post receiver 24 at the other end formounting a brake post (not shown). Each fork leg 18, 19 has an upper end26 and a lower end 28. The upper ends 26 of the fork legs 18, 19 areconnected to the crown 16 and the lower ends 28 of each of the fork legs18, 19 form a dropout 34 that has a wheel axle catch portion 36 thereon.The damping apparatus 10 of the present invention is formed for use withone of the fork legs 18, 20 and includes an upper leg 30 and a lower leg32 that slide relative to one another. The damping apparatus 10 alsoincludes a compression piston unit 368 coupled to the upper leg 30, arebound piston unit 40 coupled to the both the upper and lower legs 30,32, and an oil bed cartridge 42 engaging the compression and reboundpiston unit 38, 40. See FIG. 2. The oil is free to flow in the lower legbetween the inner and outer ends 46, 44.

The upper leg 32 of the damping apparatus 10 is preferably the upper end26 of the fork leg 18. The upper leg 30 has an outer end 44 coupled tothe crown 16, an opposite inner end 46, and a center portion 48 beingformed to define a cavity 50 between the opposite ends 44, 46.Illustratively, the center portion 48 of the upper leg 30 includes aninterior face 52 having threads 54 formed at both the outer and innerends 44, 46. The lower leg 32 of the damping apparatus 10 is preferablythe lower end 28 of the fork leg 18. See FIG. 1. The lower leg 32 has atop end 56, an opposite bottom end 58, and a generally cylindrical sidewall 60 defining a chamber 62 between the top and bottom ends 56, 58.The top end 56 of the lower leg 32 forms a rim 64 having a diametersized to receive the inner end 46 and the center portion 48 of the upperleg 30 therethrough. See FIG. 2. The outer diameter of the upper leg 30fits the inner diameter of the lower leg 32 so that the upper leg 30 isslidably engaged with the lower leg 32.

The ability of the upper leg 30 to slide into the lower leg 32 isaffected by the compression piston unit 38. In contrast, the ability ofthe upper leg 30 to slide out of the lower leg 32 is affected by therebound piston unit 40. The compression piston unit 38 includes acompression shaft 66 and the rebound piston unit 40 includes a reboundshaft 68. The shafts 66, 68 each have opposite ends 78, 80, an internalface 70 defining a passage 72, and an external face 74. Threads 75extend about the internal face 70 at the second end 80 and threads 76extend about the external face 74 at the first end 78. See FIGS. 2 and3. As shown in FIG. 2, the shaft 66 of the compression piston unit 38has a length suitable to position its second end 80 within the cavity 50of the upper leg 30. In addition, the compression piston unit 38includes a compression coupler 82 coupled to the second end 80 of theshaft 66. The shaft 68 of the rebound piston unit 40 has a length thatis less than the length of the compression shaft 66, but sufficient toposition its second end 80 within the cavity 50. The rebound piston unit40 includes a rebound coupler 84 coupled to the second end 80 of therebound shaft 68 situated within the cavity 50.

As shown in FIG. 2, the compression piston unit 38 includes a fork cap86 coupled to the first end 78 of the shaft 66 opposite the coupler 82.This cap 86 includes a threaded aperture 88 therethrough thatcorresponds with the threads 76 on the external face 74 of the shaft 66.The fork cap 86 also includes an exterior surface 90 with threads 92extending about the circumference of the surface 90. The threads 54 atthe outer end 44 of the upper leg 30 correspond with the threads 92formed on the exterior surface 90 of the fork cap 86. Thus, thecompression piston unit 38 is securely mounted in the cavity 50 of theupper leg 30.

An end plug 94 is secured in the inner end 46 of the upper leg 30. Theend plug 94 is sized for extension into the cavity 50 of the upper leg30 and includes a side wall 96 having threads 98 thereon that correspondto the threads 54 on the interior face 52 of the upper leg 30. Inaddition, the end plug 94 includes an aperture 100 therethrough that issized for slidable extension of the rebound shaft 68 therethrough.Moreover, individual tubular seals 102 are situated on the fork cap 86and at the bottom end 58 of the lower leg 32. Each seal 102 is formed tohave an aperture 104 therethrough that is sized to snugly receive therespective shafts 66, 68 therein.

The couplers 82, 84 of the respective compression and rebound pistonunits 38, 40 are formed similarly to one another. Each coupler 82, 84 isbarbell-shaped when assembled and has opposite disc-shaped ends 106, 108and a cylindrical hollow post 110 extending between the disc-shaped ends106, 108. See FIGS. 3 and 4. The outer disc 106 of each of thebarbell-shaped coupler 82, 84 is mounted on the second end 80 of therespective shafts 66, 68 and the opposite inner disc 108 extends intothe cavity 50 of the upper leg 30. The outer and inner discs 106, 108are shallow in width and circular in plan view. The outer disc 106 ofeach coupler 82, 84 has a first circle 112 engaging the second end 80 ofthe respective shafts 66, 68 and a second circle 114 engaging the hollowpost 110. The inner discs 108 each have a third circle 116 engaging thehollow post 110 and a fourth opposite circle 118. A radially outerperipheral surface 120 extends between the first circle 112 and thesecond circle 114 and a radially outer sidewall 122 extends between thethird circle 116 and the fourth circle 118 respectively.

As best shown in FIG. 2, the outer and inner discs 106, 108 are eachformed to include a central oil flow aperture 124 extending through thefirst and second circles 112, 114 and the third and fourth circles 116,118 respectively. The central oil flow apertures 124 in each disc 106,108 are in fluid communication with one another via the hollow post 110extending between the outer and inner discs 106, 108. In addition, thesidewall 122 of the inner discs 108 are each formed to include fourspaced-apart peripheral oil flow apertures 126, each in communicationwith the central oil flow aperture 124. THE hollow post 110 includesdual apertures 127 extending therethrough generally perpendicular to thecentral oil flow aperture 124. In addition, the outer discs 106 eachinclude two oil flow slots 128 in communication with the central oilflow aperture 124. The oil flow slots 128 are generally aligned with thedual apertures 127 and are positioned in a linear relation to oneanother through the fourth circle 118 and the sidewall 122 of the outerdiscs 106.

The hollow post 110 of the barbell-shaped couplers 82, 84 is preferablyintegral with the inner disc 108. The end of the hollow post 110extending away from the inner disc 108 preferably includes threads 130that are sized for engagement with the threads 75 on the internal face70 of each shaft, 66, 68. A stationary compression piston 134 and amoveable rebound piston 136 are press-fit on the hollow post 110 betweenthe discs 106, 108. The compression piston 134 and the rebound piston136 each include a mounting aperture 138 that is sized for extension ofthe hollow post 110 therethrough. The hollow posts 110 each extendthrough the mounting aperture 138 of the respective pistons 134, 136. Aspacer 132 is positioned on the post 110 to securely fasten therespective pistons 134, 136 in place. The spacer 132 on the post 110 ofthe coupler 82 mounts the piston 134 adjacent the outer disc 106. SeeFIGS. 2 and 3. The spacer 132 on the post 110 of the coupler 84 mountsthe piston 136 adjacent the inner disc 108. See FIGS. 2 and 4.

The compression and rebound pistons 136, 138 have the same configurationand each have a first face 140 more proximal to the inner disc 108 andan opposite face 142 more proximal to the outer disc 110 in theassembled damper apparatus 10. A radially outer peripheral surface orsidewall 144 of each piston 136, 138 extends between the opposite faces142. The diameter of the peripheral surface 144 is sized to fit theinner diameter of the upper leg 30. See FIG. 2. Thus, oil 42 issubstantially blocked from flowing between the side wall 144 of thepistons 136, 138 and the interior face 52 of the upper leg 30 duringcompression or extension between the upper and lower legs 30, 32. Thepistons 136, 138 are each formed to include three spaced-apart slots 146extending through the opposing faces 140, 142. See, for example FIG. 5.In addition, three angled apertures 148 are Situated through theopposing faces 140, 142 in a spaced-apart relationship to one anotherbetween the three slots 146. The apertures 148 are defined by oppositemouths 150, 152. The apertures 148 are angled in a manner that positionsthe first mouth 150 through the first face 140 of the pistons 136, 138adjacent the mounting aperture 148 and the opposite step-up mouth 152 ina position that overlaps the second face 142 and the outer periphery144. It is understood that greater than or less than three slots 146 orapertures 148 may extend through the pistons 134, 136 so long as thereis at least one slot or aperture therethrough.

As best shown in FIG. 3 the compression piston 134 is formed to bemounted on the hollow post 110 of the coupler 82 adjacent the outer disc106. A movable valve 154 is positioned on the hollow post 110 betweenthe face 142 of the piston 134 and the inner disc 108. A spring 156normally biases the valve 154 against the first face 140 of the piston134. The movable valve 154 preferably has a diameter substantiallyequivalent to the diameter of the inner disc 108. Thus, the diameter ofthe movable valve 154 is sufficient only to cover the mouths 150 of thethree apertures 148. A shim 158 is positioned on the hollow post 110between the second face 142 of the piston 134 and the outer disc 106 ofthe coupler 82. The shim 158 has a diameter that is slightly less thanthe diameter of the piston 134. Thus, the shim 158 substantially coversthe spaced-apart slots 146, but leaves the step-up mouths 152 of theapertures 148 open. Preferably the apparatus 10 includes a shim stack159 between the piston 134 and disc 106. The stack 159 includes shims158, 161, 163, 169 that decrease in size as they are stacked from thepiston 134 to the outer disc 106. It is understood that the number,order, and size of shims in the stack 159 may be varied to accommodateriders of different weight and to alter the compression damping of theapparatus 10.

The shim 158 is not movable and although the moveable valve 154 does notcover the three slots 146, the shim 158 permanently blocks threespaced-apart slots 146 extending through the piston 134 from oil flowtherethrough. Importantly, the mouth 152 of the three apertures 148remains open through the second face 142. The three apertures 148 areopened through the first face 140, of the piston 134, however, only whenthe fluid flow pressure is such that the valve 154 is moved against thespring 156 toward disc 108.

Referring now to FIG. 4, the rebound piston 136 is mounted on the hollowpost 110 of the coupler 84 adjacent the outer disc 106. A movable valve160 is positioned on the hollow post 110 between the outer disc 106 andthe piston 136 and is normally biased against the second face 142 of thepiston 136 by a spring 162. This movable valve 160 has a diameter thatis slightly less than the diameter of the piston 136. Thus, the moveablevalve 160 selectively covers the three spaced-apart slots 146. A shim164 is positioned on the hollow post 110 between the first face 140 ofthe piston 136 and the inner disc 108 of the coupler 84. The shim 164has a diameter that is substantially equivalent to the diameter of theinner disc 108. Thus, the shim 164 only covers the mouths 150 of thethree apertures 148. The shim 164 is pressed against the piston 136 andtherefore covers the mouths 150 of the three angled apertures 148. Inpreferred embodiments, a shim stack 165 is situated between the piston136 and the disc 108. The shim stack 165 includes shim 164 and shim 167.Shim 167 has a diameter that is less than shim 164. It is understoodthat the number, order, and size of shims in stack 165 may be changed tomanipulate the stiffness of the rebound.

The damping apparatus 10 of the present invention further includes acompression adjustment mechanism 166 and a rebound adjustment mechanism168. The mechanisms 166, 168 each cooperate with the respective couplers82, 84. Each of the adjustment mechanisms 166, 168 include a needle 170having a pointed end 172, an opposite end 174, a cylindrical side wall176 extending between the ends 172, 174, and a knob 178 coupled to theopposite end 174 of the needle 170. Illustratively, the pointed end 172of the needle 170 is positioned adjacent the respective coupler 82, 84and the knob 178 is coupled to the opposite end 174 of the needle 170 bya screw 180. It is understood, however that pins, rivets, staples,adhesives, and other well known attachment means may be used to coupledthe knob 178 to the needle 170. Illustratively, spaced-apart seals 183are situated on the side wall 176 threads 181 extend about thecylindrical side wall 176 of the needle 170.

The passage 72 in each of the shafts 66, 68 of the compression and therebound units 38, 40 is sized to receive the needle 170 therein. Thepassage 72 is formed to include a first section 182 having a firstdiameter sized to receive the side wall 176 of the needle 170 thereinand a second section 188 extending from the first section 182. Inpreferred embodiments, grease or oil is provided in the passage 72 toprovide lubrication for manipulating the needle 170 in the first section182 of the passage 72. The third section 188 is formed to have adiameter that is greater in size than the diameter of the first section182. The third section 188 is sized to receive the knob 178 therein andincludes threads 190 about its periphery that are formed to correspondwith the threads 181 on the needle 170.

The compression piston unit 38 allows a user to adjust the stiffness ofthe bicycle fork 12. This adjustment is achieved by turning the knob 178of the compression adjustment mechanism 166. The knob 178 selectivelydrives the needle 170 up or down in the passage 72 to adjust thepositing of the pointed end 172 of the needle 170 in the hollow post 110of the coupler 82. This relative positioning alters the flow diameter ofthe oil flow aperture 124 and thus the ability of the oil 42 to flowthrough the piston 134.

Adjustment of the knob 178 reduces the flow of fluid through thecompression piston 134 for small bumps and thus stiffens the compressionresponse of the bicycle fork 12. The oil flow aperture 148 remains open,however, so with large bumps, the upward pressure of the lower leg 32 asshown by arrow 192 forces the flow through the apertures 127 and pastthe compression piston 134 as shown by arrows 202. See FIG. 6. Thus, theupper leg 30 moves into the outer leg 32 and thus absorbs the shock ofthe large bump.

The rebound piston 136 beneficially allows the user to individuallyadjust the speed/stiffness of the rebound of the bicycle fork 12. Thisadjustment is achieved by turning the knob 178 of the rebound adjustmentmechanism 166. Turning the rebound assembly knob 178 drives the needle170 up or down in the passage 72 to adjust the positioning of thepointed end 172 of the needle 170 in the hollow post 110 of coupler 84.The extent to which the needle 170 is positioned in the post 110 altersthe flow diameter of the aperture 124 and thus the rate of fluid flowthrough the coupler 84. Therefore, as the needle 170 is adjusted toreduce the diameter of the aperture 124, fluid slowed as it passes intothe two oil flow slots 128 in the outer disc 106 of the coupler 84 thusslowing the rebound of the fork 12.

The relative positioninig of the compression coupler 82 and the reboundcoupler 84 within the cavity 50 of the upper leg 30 in the assembleddamping apparatus 10 creates three flow zones within the cavity 50. Thefirst normal zone 194 is situated in the cavity 50 between the innerdisc 108 of the compression coupler 82 and the inner disc 108 of therebound coupler 84. The second compression zone 196 is situated betweenthe second face 142 of the piston 134 and the fork cap 86 mounted in theouter end 44 of the upper leg 30. The third rebound zone 198 is situatedbetween the second face 142 of the rebound piston 136 and the inner end46 of the upper leg 30. It is understood that the volumetric size of thesecond compression zone 196 is constant, but the volumetric size of thefirst normal zone 198 and the third rebound zone 198 vary depending uponthe relative positioninig of the upper leg 30 within the chamber 62 ofthe lower leg 32.

In operation, when the bicycle fork 12 encounters a bump force, thelower leg 32 is forced upwardly as shown by arrow 192. This upwardlymovement forces the upper leg 30 into the chamber 62 of the lower leg32, causing the rebound piston 136 to move toward the stationarycompression piston 134 within the cavity 50 of the upper leg 30.Movement of the rebound piston 136 toward the compression piston 134reduces the volumetric size of the first normal zone 194, forcing theoil bath 42 to displace to make room for the rebound shaft 68. The oil42 is displaced through the peripheral and central oil flow apertures126, 124 in the inner disc 108 and out from the aperture 127 into thesecond compression zone 196, creating compression damping as shown byarrows 202.

The rebound piston 136 does not substantially effect this compressiondamping. On a compression stroke of the fork leg 18, as shown by arrow192, the rebound piston 136 and the movable valve 160 cooperate to actas a blow-off valve to eliminate a vacuum effect within the cavity 50.The piston 136 and valve 160 serve to minimize the effect of the reboundpiston 136 on the compression damping. As shown in FIG. 6, oil flow intothe spaced-apart slots 146 in the first face 140 of the rebound piston136 forces the movable valve 160 to move against spring 162 away fromthe second face 142 of the piston 136. Oil is free to flow, as shown byarrow 200 into the third rebound zone 198 as the upper leg 30 moves intothe chamber 62 of the lower leg 32.

When compression force is relieved, a compression spring (not shown) inthe opposite fork leg 19 presses on the lower leg 32 away from the crown16. This movement is transferred to the first fork leg 18 through thedropouts 34 that are commonly mounted on a bicycle wheel (not shown).The speed at which the compression spring (not shown) is able to pressthe lower leg 32 away from the crown 16 is adjusted by the reboundadjustment mechanism 168 in the lower leg 32 of fork leg 18.

Rebound damping is achieved by oil transferring from one side of therebound piston unit 40 to the other. See arrows 205. The movable valve160 is pressed against the second face 142 of the piston 136 during theexpansion stroke. See FIG. 7. During expansion an stroke the compressionpiston 134 and the movable valve 154 cooperate to act as a blow-offvalve and permit rapid fluid flow through the spaced-apart apertures 148in the piston 134. Oil flow into the apertures 148 in the second face142 of the compression piston 134 forces the movable valve to moveagainst spring 156 away from the first face 140 of the piston 134. Oilis free to flow as shown by arrow 203 back in to the first flow zone 194as the upper leg 30 moves out of the chamber 62 of the lower leg 32.

In an alternative embodiment of the present invention, a dampingapparatus 210 is provided that includes an upper leg 230 that is formedfor slidable extension into the lower leg 32. See FIG. 8. The upper leg230 includes opposite ends 244, 246, a center portion 248 that is formedto include an interior face 252 that defines a cavity 250 and that formsa valve seat 253 thereon. The damping apparatus 210 also includes acompression piston unit 238 situated within the cavity 250 of the upperleg 230 and the adjustable rebound piston unit 40 illustrated in FIG. 2.The unit 40 is coupled to the lower leg 32 and formed to extend into thecavity 250 of the upper leg 230.

The cavity 250 of the upper leg 230 is formed in three zones 252, 254,256 that correspond generally with the normal first flow zone 194, thesecond compression zone 196, and the third rebound zone 198 respectivelyof the apparatus 10. The compression piston unit 238 is semi-press fitagainst the valve seat 253 in the first zone 252 and the rebound pistonunit 40. The compression unit 238 includes a compression coupler 282having a compression piston 240 and shim stack (not shown) mountedthereon. The compression coupler 282 is formed in the same manner ascoupler 82, except that coupler 82 has threads 130 for secure engagementwith the shaft 66.

In operation, upon experiencing the force of a bump, the lower leg 32moves over the center portion 244 of the upper leg 230. This movementforces the rebound shaft 68 into the cavity 250 toward the valve seat253 and the oil 42 to flow through the compression piston unit 238 aspreviously described into the compression zone 254. Since the apparatus210 lacks a compression adjustment mechanism, the amount of compressiondamping cannot be adjusted by the bicycle rider. The apparatus 210 does,however, include the rebound adjustment mechanism 168. Thus, the oilfreely flows through the slots 146 formed in the rebound piston 136 aspreviously described into the third zone 256 during compression of theapparatus 210. During expansion movement, however, the oil 42 must flowsubstantially through the central oil flow aperture 124 of the coupler84. The speed of this flow is altered by driving the needle into and outof the passage 72 of the shaft 68.

In yet another alternative embodiment of the present invention, adamping apparatus 310 is provided that includes the upper leg 230 thatis formed for slidable extension into the lower leg 32. See FIG. 9. Theupper leg 230 is formed as previously described and the compressionpiston unit 238 is semi-press fit against seat 253 within the first zone252 of the cavity 250. The damping apparatus 310 also includes a reboundpiston unit 340 coupled to the lower leg 32 and formed to extend intothe cavity 250 of the upper leg 230.

The rebound piston unit 340 includes the coupler 40, the rebound shaft68, and the rebound piston 136 as previously described. In preferredembodiments, the shaft 68 is solid. It is understood however that thecentral oil passage 124 through the outer disc 108 could also be sealedto prevent oil therethrough. Since the apparatus 310 lacks a compressionadjustment mechanism and a rebound adjustment mechanism, the bicyclerider will not have the ability to adjust the amount of compressiondamping or rebound damping without dissembling the apparatus or changingthe weight of the oil.

Ideally, the damping system of the present invention is designed withthe compression spring (not shown) in one leg of the fork 19 and thedamping apparatus 10 in the other leg 18, but a fork 12 can be designedto work with springs on both legs 18, 19 by mounting an external spring(not shown), similar to a rear shock, or by mounting the springsunderneath the inner leg 30, inside the chamber 62 outer leg 32.

FIGS. 10 and 11 illustrate the operation of the rebound piston unit whena flexible valve 160 is utilized. As shown in FIG. 10, when acompression force, indicated by arrow 192, causes a relatively lowvelocity movement of lower leg 32 on a compression stroke, damping fluidwill pass through slots 146 and push valve 160 against spring, 162. Forthese low velocity movements, valve 160 will not fully compress spring162, as moving valve 160 part way along post 110 of coupler 84 providessufficient blow-off on the compression stroke.

On high velocity movements of lower leg 32 on the compression stroke,damping fluid will flow through slots 146 as shown and press valve 160against extended walls 106 a, which have been added to disc 106. As thepressure of the damping fluid against valve 160 increases, valve 160will flex as shown, thereby providing smoother compression damping.

FIGS. 12 and 13 show another embodiment of a compression piston unit. Inthis embodiment, a shaft 366 b is disposed within shaft 366 a. Shaft 366b terminates in a first stop 366 c. A passage 366 d extends along theinterior of shaft 366 b and includes a lower aperture 366 e and an upperaperture 366 f. The longitudinal axis of passage 366 d is generallyparallel to and generally coincident with the longitudinal axis of shaft366 a and 366 b. Apertures 366 e and 366 f are generally transverse tothe longitudinal axis of passage 366 d. Needle 370 extends down throughshaft 366 b and is adjustable with respect to aperture 366 f in a mannersimilar to that described above for needle 170 in the embodiment of FIG.2. A second stop 366 g is attached to the lower end of shaft 366 a. Stop366 g can be secured to shaft 366 a in any number of ways, includingthreading it into shaft 366 a. A spring 356 b is disposed about stop 366g. Piston 334 includes slots 346 (not shown) and apertures 348 (also notshown) corresponding to slots 146 and apertures 148 in the embodiment ofFIG. 3. A central bore is provided through lock nut 306, disk 308, post310, piston 334, valve 354 and the various shims in shim stack 359 toaccommodate shaft 366 b. Note that disk 308 includes a tapered innerarea 308 a. Disk 308 may be provided with oil flow aperturescorresponding to apertures 126 of the embodiment of FIG. 3. An o-ring orsimilar seal 334 a is provided in piston 334 and rides along shaft 366b, as described below.

In its initial, uncompressed state, piston 334 is at the lower end ofshaft 366 b such that disk 308 rests on stop 366 c. As a compressionforce, as indicated by arrow 192, is applied to the lower leg (notshown), the lower leg and its rebound shaft will enter upper leg 330thereby displacing damping fluid upwardly. As this occurs, piston 334and the other components joined by coupler 382 begin to rise along shaft366 b. As this occurs, the tapered area 308 a within disk 308 slowlyexposes aperture 366 e, thereby allowing damping fluid to flow withinpassage 366 d and through aperture 366 f. Note that as piston 334 rises,valve 354 remains against piston 334 and seals off apertures 348 (notshown). Likewise, the members of shim stack 359 remain disposed overslots 346. As the damping fluid continues to rise, piston 334 willeventually raise to the point where lock nut 306 abuts stop 366 g. Atthis point, an increase in the damping fluid pressure will cause dampingfluid to flow through slots 346 and past the shims in stack 359, asshown. Note that damping fluid also continues to flow in aperture 366 e,through passage 366 d and out aperture 366 f. The compression dampingcan be controlled in various ways, as by adjusting needle 370.Similarly, compression damping can be adjusted by shortening orlengthening stop 366 g such that lock nut 306 engages it earlier orlater in the compression stroke. Alternatively. shafts 366 b of variouslengths can be utilized, thereby again effectively controlling when inthe compression stroke lock nut 306 will engage stop 366 g.

FIGS. 14 and 15 show yet another embodiment of the present invention.This embodiment differs from that of FIGS. 12 and 13 in that a stop 466a is attached to the lower end of shaft 366 a and supports a stationarycompression piston 434 and its associated components. A passage 410 aextends through disk 408, post 410 and disk 406. Passage 410 a has anaperture 410 b at one end thereof and an aperture 410 c at the otherend. Disk 408 may be provided with openings corresponding to oil flowapertures 126 in the embodiment of FIG. 3. Piston 434 includes slots 446(not shown) and apertures 448 (not shown). A needle or set screw 410 eis provided in disk 406 transverse to the axis of passage 410 a. Needleor set screw 410 e may be used to adjust the amount of bleed throughaperture 410 c in a manner similar to the use of needle 370.

In this embodiment, as a compression force, indicated by arrow 192, isapplied, the damping fluid will rise within leg 330 and flow fromaperture 410 b through passage 410 a and out aperture 410 c. Likewise,damping fluid will flow past the shims in stack 459. As fluid flows tothe same side of piston 434 as piston 334, piston 334 will rise alongshaft 366 a in the manner described with respect to the embodiments ofFIGS. 12 and 13. As this occurs, aperture 366 e will be exposed anddamping fluid will flow from that aperture through passage 366 d and outaperture 366 f. When piston 334 has reached its maximum range of travel(FIG. 15), oil will flow through piston 334 and past the shims in stack359, as described above. Again, by adjusting the length of shaft 366 aand the lengths of stops 366 g and 466 a, the point in the compressionstroke at which the various pistons, passageways and apertures come intoplay call be controlled. Note that the embodiment of FIGS. 14 and 15could also be modified such that both compression piston assemblies 334and 434 are stationary. This is schematically shown in FIG. 16.

Although the apparatus has been described with reference to particularmeans, materials and embodiments, from the foregoing description, oneskilled in the art can easily ascertain the essential characteristics ofthe illustrative apparatus and various changes and modifications may bemade to adapt the various uses and characteristics without departingfrom the spirit and scope of the present invention as described by theclaims which follow.

What is claimed is:
 1. A bicycle fork having a damping apparatus, thedamping apparatus comprising: a cylinder defining a chamber; a shaftdisposed in the chamber; a piston disposed in the chamber and coupledwith the shaft and being movable relative to the shaft between first andsecond positions, the piston having a fluid flow aperture disposed therethrough and a valve structure associated with the piston, the valvestructure being movable between engaged and disengaged positions, thefluid flow aperture being occluded when the valve structure is engagedand the fluid flow aperture being exposed when the valve structure isdisengaged; wherein the piston is a floating piston; damping fluidlocated in the chamber; the piston being movable from the first positionto the second position as a result of an external force being applied tothe fluid which acts on the piston; and when the piston is in the secondposition, the fluid is caused to move through the fluid flow apertureand move the valve structure to the disengaged position.
 2. The dampingapparatus of claim 1, wherein the shaft further comprises first andsecond apertures in communication with each other, and each aperturepositioned on opposed sides of the piston.
 3. The damping apparatus ofclaim 2, wherein the first aperture is occluded when the piston is inthe first positioned and exposed when the piston is in the secondposition.
 4. The damping apparatus of claim 1, further comprising a biasmember associated with the piston.
 5. A bicycle fork having a dampingapparatus, the damping apparatus comprising: a cylinder; a damping fluidlocated in the cylinder; a floating piston disposed in the cylinder andpositioned adjacent the fluid; a second piston located within thechamber; and a second shaft located in the cylinder and associated withthe second piston.
 6. The damping apparatus of claim 5, furthercomprising a bias member associated with the floating piston.
 7. Thedamping apparatus of claim 6, wherein a shaft is disposed within thecylinder and associated with the piston.